A process for imparting a vitreous structure, i.e., one which fails to exhibit any crystalline structure on X-ray exposure ("Les verres metalliques" (Metal glasses), Praveen Chaudhari, Bill Giessen and David Turnbull, "Pour la Science," June 1980, No. 32, p. 68), and Scientific American, Vol. 242, No. 4, at 84-96 (April 1980) by cooling certain molten metals or alloys at very high speed, i.e., rapid quenching, of the order of 10.sup.6 .degree.C./second, is known.
Such process for producing an amorphous metallic structure generally comprises projecting a jet of molten metal, which spreads in the form of a very thin layer over a cooled surface that is a good heat conductor and which is moving at high speed.
Different processes of solidification on cold moving surfaces have been proposed in the prior art. For example, these processes include, among others, solidifying the metal in the following ways, inside a wheel, on a drum, on a disk and between two rollers. The simplest and most commonly used method consists of projecting a jet of molten metal over the outside surface of a cold metal wheel turning at high speed. The molten metal, ejected under pressure from a crucible, forms a stationary bulb on contact with the wheel which produces a rapidly solidified metal strip. The latter, under the effect of centrifugal force, separates from the cold wheel and is ejected.
Studies made of these different types of processes have revealed the influence of the boundary gaseous layer in contact with the cold surface on the quality of the edges and surface state of the metallic strip.
These studies have led to proposals of operating under a controlled atmosphere and, notably, under low pressure, by placing all of the equipment in a closed vessel. One major disadvantage of this technique, however, resides in the volume of the vessel to be built, particularly when the process is used on an industrial scale. Moreover, when a vacuum is applied to the system, it cannot be applied continuously because the vacuum is necessarily broken every time the strip produced is to be recovered. In addition, it has been found that, in the process of rapid solidification on a wheel, separation of the strip takes place more rapidly when operating under vacuum than when the process is conducted in the open, and that solidification is less intense.
It is, of course, possible to contemplate rapidly solidifying hyperhardening under vacuum and continuously bringing the strip out of the vessel, but it is difficult to adapt a vacuum vessel to a very fast-turning wheel which permits the maintenance of a satisfactory continuous vacuum, while allowing the strip to emerge into the atmosphere, especially in view of the fact that separation of the metal strip from the wheel is an unstable phenomenon.
This serious disadvantage, in particular, led to the search for a technique of rapid solidification under a controlled atmosphere which did not involve centrifugal force, and with that end in view, use of the method of rapid solidification on a moving band, passing at great speed under the jet of molten metal. This method, known in principle, presents appreciable disadvantages, principally among which are the vibrations of the supporting band and, in general, the imprecision of its positioning, resulting, in particular, from its fast-turning pulley drive, the difficulty of cooling the band effectively and a greater complexity of use than rapid solidification on a wheel.